Tiny386

Introduction

Tiny386 is a x86 PC emulator written in C99. The highlight of the project is its portability. It now boots Windows 9x/NT on MCU such as ESP32-S3.

The core of the project is a built-from-scratch, simple and stupid i386 cpu emulator. Some features are missing, e.g. debugging, hardware tasking and some permission checks, but it should be able to run most 16/32 bit softwares. To boot modern linux kernel and windows, some 486 and 586 instrutions are added. The cpu emulator is kept in ~6K LOC. There is also an optional x87 fpu emulator.

To assemble a complete PC system, we have ported many peripherals from TinyEMU and QEMU, it now includes:

• 8259 PIC
• 8254 PIT
• 8042 Keyboard Controller
• CMOS RTC
• ISA VGA with Bochs VBE
• IDE Disk Controller
• NE2000 ISA Network Card
• 8257 ISA DMA
• PC Speaker
• Adlib OPL2
• SoundBlaster 16

For firmwares, the BIOS/VGABIOS comes from seabios. Tiny386 also supports booting linux kernel directly, without traditional BIOS. The idea comes from JSLinux, and it uses a small stub code called linuxstart.

Demo

See here

Build

Linux: You need to install SDL1.2 or sdl12-compat first, then type make.

For other platforms, please refer to .github/workflows/build.yml.

Pre-built binaries: here

Usage

• Prepare an ini file

[pc]
; set path to BIOS and VGA BIOS
bios = bios.bin
vga_bios = vgabios.bin

; set memory size and VGA memory size
mem_size = 32M
vga_mem_size = 2M

; fda/fdb for floppy disks (optional)
fda = floppy.img

; hda/hdb/hdc/hdd for hard disks (optional)
; cda/cdb/cdc/cdd for CD-ROM disks (optional)
hda = win95.img
cdb = win95_cd.iso

; "fill_cmos" fixes "MS-DOS compatibility mode" in win9x, but it breaks winNT...
fill_cmos = 1

[display]
width = 720
height = 480

[cpu]
; gen = 3/4/5, for 386/486/586
gen = 3
; fpu = 0/1, to disable/enable x87
fpu = 0

• Run

./tiny386 config.ini

ESP32 port

Currently the only supported target is the JC3248W535 dev board. The supported ESP-IDF version is v5.2.x.

Build and Flash

You can find the pre-built flash image esp/flash_image_JC3248W535.bin from here. The pre-built image can be flashed directly at offset 0.

To build and flash manually:

scripts/build.sh patch_idf  # apply patches to ESP-IDF
cd esp
idf.py build
idf.py flash

Configure

All files should be put in a SD card with FAT/exFAT file system. The ini file should be tiny386.ini and put in the root directory. Please refer to esp/tiny386.ini.

Keyboard/Mouse Input

There is no input device on the dev board, so currently wifikbd is used to forward keyboard/mouse events to the dev board over WIFI:

(EEP32-S3 board: listen on TCP port 9999) <--- WIFI ---> AP <--- WIFI/Wire ---> (PC: ./wifikbd esp_board_addr 9999)

License

The cpu emulator and the project as a whole are both licensed under the BSD-3-Clause license.